Detection limits in the NACO L′ (top panel) and M′ (bottom panel) filters. Solid lines are the azimuthally averaged limits and the shaded areas are the variance of the six azimuthal positions. The limits are calculated with a mean and PCA-based background subtraction for both filters. A range of PCs was tested but only the limits with the highest sensitivity are presented. The black dashed lines show the false positive fraction (right axis) associated with the detection limits and the horizontally dotted lines indicate the apparent magnitude in the background-limited regime. The black crosses show the separation and contrast of β Pic b as determined with the MCMC analysis (the uncertainties are smaller than the symbol size).